1. Field of the Invention
The present invention relates to a wire bonding apparatus and more particularly to a wire bonding apparatus that is equipped with a movable torch electrode.
2. Prior Art
In movable torch electrode systems, a torch electrode is moved horizontally. The torch electrode is moved and positioned beneath the tip end of a wire that extends out of the tip end of a capillary. The electrode is caused to discharge so as to form a ball at the end of the wire. When the ball is formed once, the torch electrode is withdrawn from beneath the capillary.
Examples of wire bonding apparatus equipped with a movable torch electrode of this type are described in Japanese Patent Application Publication (Kokoku) No. H1-58861 and Japanese Patent Application Laid-Open (Kokai) No. H9-205110.
In Japanese Patent Application Publication (Kokoku) No. H1-58861, the movable electrode is horizontally provided beneath the capillary through which a wire passes so that a ball is formed at the end of the wire by electrical arc effected by the movable electrode.
In Japanese Patent Application Laid-Open (Kokai) No. H9-205110, the movable torch electrode system comprises a horizontal actuating arm to which a torch electrode is installed so that the horizontal actuating arm is moved horizontally, a spring which pulls this horizontal actuating arm toward the area beneath the capillary, a stopper which positions the horizontal actuating arm beneath the capillary, and an actuator that is a solenoid and drives the horizontal actuating arm so that the torch electrode is withdrawn from beneath the capillary.
When the solenoid is switched on, the horizontal actuating arm is pulled by the magnetic force of the solenoid, and the arm is withdrawn from beneath the capillary. When the solenoid is switched off, the horizontal actuating arm is caused to move beneath the capillary by the driving force of the spring and stops when the arm comes into contact with the stopper.
In this prior art, the torch electrode is stopped by being brought into contact with the stopper. Accordingly, noise is generated, and dust is likely caused by wear. Furthermore, the range of movement of the torch electrode is limited by the solenoid and stopper. Thus, there is no degree of freedom in the position of the torch electrode, and the torch electrode becomes an obstruction, resulting in poor working characteristics so that passing the wire through the capillary and replacing the capillary cannot be done easily. Furthermore, since the system uses a spring and solenoid, high-speed operation cannot be achieved.